Last weekend, millions of Americans took to the highways in search of one last summer respite before the onset of fall. In doing so, they drove straight into a statistical and behavioral slalom course. Consider the Labor Day scenario. Will you knock off work for the whole day Friday and leave during morning rush-hour traffic, or wait until long after sunset to avoid the rush? If you wait until nightfall, will you have a beer—just one, of course—with your colleagues before you hit the road? If you leave early, will you bring your BlackBerry along to stay in touch with your boss in case something comes up at the office? If you’re a man, will you bring a female companion along as a passenger or to share the driving, or will you drive alone, or with a few male friends, perhaps because you’re divorced? Will you drive a nimble black Mini Cooper S or a huge red F-150 pickup? Is your car (or truck) new or old?

Tom Vanderbilt’s data-heavy new book, Traffic, explains how each of these decisions or conditions (like whether you’re a man or a woman) dramatically changes the odds of getting yourself killed, or killing someone else, in a horrific crash. Note that these variables don’t change the statistical odds of whether you’ll live or die; your chances of living through the commute are always vastly better than those of dying (though there’s probably some exception out there). Over a lifetime of driving, the “average person” has about a 1 in 100 chance of dying in a car crash, which means that you’re likely to see yet another workweek. Still, driving is the most dangerous thing that most of us will ever do on a regular basis.

And as it turns out, there really is no “average” driver. The “average person” of the 1-in-100 probability is really just a nonexistent person made up of all of the wildly different types of drivers out there, whose crash risks differ wildly, too. Similarly, there is no statistically “safest” car or truck to drive; your car or truck is what you make of it. Just as each of us, in this iPod age, may have a customized playlist of drive-time music, each of us also has a customized risk of drive-time harm.

For example, Vanderbilt writes that “a young man is 100 times more likely than a middle-aged woman to be killed in traffic.” A person “driving on Sunday morning at three AM”—still Saturday night to many drivers on the road, of course—“has a risk 134 times greater than someone driving at 10 AM on Sunday” of being killed. Everyone knows that being drunk is a big risk, but that doesn’t necessarily mean legally drunk: a blood-alcohol level of just .02, one-fourth the legal drunk-driving threshold in many states, hikes the likelihood of a crash. And “someone with a personality disorder is 10 times more likely to have a serious crash,” the author notes.

All of these risk factors add up. In the words of one of Vanderbilt’s many research sources, traffic-risk expert John Adams, you could conclude, with a few caveats, that “a disturbed, drunken young man on the road on a Sunday morning was about 2.5 million times more likely to have a serious accident than a normal, sober, middle-aged woman driving to church seven hours later.” Even seemingly small factors have a big impact. A man with a woman riding shotgun, for instance, is less likely to crash. A divorced man is more likely to crash than a married man.

While it’s easy to see why a drunken 17-year-old male has a greater chance of crashing than a young grandmother, a few of Vanderbilt’s stats are nonetheless eye-opening. For one thing, despite the real danger that other vehicles pose, drivers must more often guard against the enemy within. Most fatal crashes are single-car crashes: people fall asleep or send a text message and go zooming right off the road. Most people think that they’re above-average drivers, perfectly capable of chatting on a cell phone or skipping that needed rest time because of their superior abilities. But in driving, as in anything, somebody has to be below average.

Auto engineering, too, is really an exercise in psychological engineering. Maybe you bought an SUV for your family a few years back, and even though you’ve hated paying more at the pump over the past year, you still figure it’s the safest vehicle to have in case you get hit by a big truck on the highway. But, Vanderbilt points out, SUV drivers simply swap safety advantages “for more aggressive driving behavior. The results, studies have argued, is that SUVs and small trucks are, overall, no safer than medium or large passenger cars.” The same proves true for drivers of newer cars with superior safety features. They drive more dangerously, figuring that the car will protect them. That’s why innovative safety features, while they do save some lives, often save far fewer lives than originally projected. Conversely, people often greet a truly dangerous situation by driving much more safely. In snowstorms, for example, while minor crashes abound, there are actually fewer fatal crashes, because drivers are that much more cautious.

As for the role of traffic-safety regulations, Vanderbilt quotes a Netherlands traffic engineer, Hans Monderman, who decries “how foolish are we in always telling people how to behave. When you treat people like idiots, they’ll behave like that.” A naive engineer might think that a good way to stop speeding through a small village is to put up dozens of traffic signs forbidding such speeding. But too many street signs actually make people focus only on the road and forget that there are people and houses nearby. In the Dutch town of Makkinga, Monderman removed all street signs and engineered roads so that drivers would remember the “social world” outside, rather than just the “traffic world.” It worked: drivers’ speeds slowed markedly, heartening the mothers of playing children, as the drivers took cues from their environment rather than the signs. Some studies have shown that unmarked rotary intersections, which are often viewed as more complicated and thus more dangerous than intersections directed by lights, have lower crash rates.

Another lesson in the economic law of unintended consequences: New Yorkers have read a lot in the last few years about the scourge of cheap on-street parking. By encouraging people to drive around in circles looking for a spot, critics say, on-street parking causes pollution, and it also causes up to 20 percent of urban crashes. So why not just take the free parking away? Well, it’s not so simple. Some studies show that “rows of parked cars actually make things safer for pedestrians,” Vanderbilt writes, because the stress of driving in a small space, menaced by opening and closing doors, prompts drivers to slow down. Plus, with a parked-car buffer, moving cars are more likely to crash into one another rather than into pedestrians.

And while Gotham obviously needs its street signals and the like, New Yorkers, like everyone else, should remember to use their heads and not rely on technology. “More pedestrians are killed in New York City while obeying the law”—by walking in crosswalks with the light—than while breaking it, Vanderbilt reminds us, because people are paying attention to the sign saying WALK rather than to the car barreling around the corner, its driver jabbering obliviously on a cell phone. In short: first-world cars and roads are already so safe, relatively, that any improvements are marginal, have less dramatic effects, and can easily be wiped out by individual behavior.

While clear, well-enforced rules don’t solve everything, they’re better than having no rules at all—as a comparison of first-world and third-world auto-safety stats shows. In this light, car safety is a window on global economics and governance. After all, laws and enforcement of laws, whether governing traffic or property rights, vary widely across nations, with the differences often related to national income and national culture. In developing countries, fatal and other serious auto-crash rates go up quickly at first, rising with GDP and with the rate of car ownership, but then level off once a country reaches a per-capita income of $18,000 per person, because citizens in richer countries are more aware of road danger and demand government action.

Varying auto-safety rates among nations go beyond mere economics, though. Crash stats in the Netherlands are markedly better than in Belgium, even though the two countries have similar per-capita incomes and auto regulations. Vanderbilt chalks up the difference at least partly to corruption: in Belgium, people can fix their way out of a ticket through personal connections or just plain wheedling, and hence drive more recklessly. Uganda and Nigeria, with low per-capita GDPs, are two of the most dangerous places to drive, not only because of horrible roads and cars but because of dishonest government, too.

We learn to drive, just as we learn to do anything, partly by becoming accustomed to the unexpected and dealing with it effectively. On a one-way street, drivers don’t expect to see a car coming from the other direction; it’s how we act when one does that’s most important. Our familiarity with driving, and our understanding that the road always offers surprises, is partly why a book about traffic is so useful in offering lessons for the rest of life. There’s a lesson applicable to financial regulation: make markets safer through rules and enforcement, but remember that such safety could cause people to act in a riskier manner. And there’s a lesson about terrorism: a driver is vigilant after a crash, just as a nation is vigilant after an attack—but it’s difficult and tiresome to be vigilant all the time.

As Vanderbilt writes, “many of us spend more time in traffic than we do eating meals with our family, going on vacation, or having sex.” We may as well learn something from it—and thanks to his fascinating and original book, we can.

Nicole Gelinas, a City Journal contributing editor and the Searle Freedom Trust Fellow at the Manhattan Institute, is a Chartered Financial Analyst.